The body includes various passageways such as arteries, other blood vessels, and other body lumens. These passageways sometimes become occluded or weakened. For example, the passageways can be occluded by a tumor, restricted by plaque, or weakened by an aneurysm. When this occurs, the passageway can be reopened or reinforced, or even replaced, with a medical endoprosthesis. An endoprosthesis is typically a tubular member that is placed in a lumen in the body. Examples of endoprosthesis include stents and covered stents, sometimes called “stent-grafts”.
An endoprosthesis can be delivered inside the body by a catheter that supports the endoprosthesis in a compacted or reduced-size form as the endoprosthesis is transported to a desired site. Upon reaching the site, the endoprosthesis is expanded, for example, so that it can contact the walls of the lumen.
The expansion mechanism may include forcing the endoprosthesis to expand radially. For example, the expansion mechanism can include the catheter carrying a balloon, which carries the endoprosthesis. The balloon can be inflated to deform and to fix the expanded endoprosthesis at a predetermined position in contact with the lumen wall. The balloon can then be deflated, and the catheter removed.
In another delivery technique, the endoprosthesis is formed of an elastic material that can be reversibly compacted and expanded. During introduction into the body, the endoprosthesis is restrained in a compacted condition. Upon reaching the desired implantation site, the restraint is removed, for example, by retracting a restraining device such as an outer sheath, enabling the endoprosthesis to self-expand by its own internal elastic restoring force.
One method of making a stent includes laser cutting a tube of stent material to define the structure of the stent. Laser cutting, however, can form recast material, which is material from the tube that has melted, oxidized, and solidified on laser-cut surfaces. The recast material can make a stent more susceptible to failure (e.g., cracking or fracture) during manufacturing or in use. Accordingly, sometimes, the recast material is removed, e.g., by chemical milling and/or electropolishing, after laser cutting. To compensate for loss of material during the removal step(s), the metal tube can be made oversized, which can be wasteful and costly, particularly if the tube includes precious metals. The removal step(s) may also include using potent and/or hazardous chemicals.